1. Field of the Invention
The invention relates to a retainer for a printing plate on a plate-carrying cylinder of a rotary printing press. In particular, the invention relates to a device having a hook engageable in an elongated slot formed in the plate-carrying cylinder and terminating in an outer circumferential surface thereof, the hook being fixedly connected to a tension rod that is rotatably supported in a first elongated bore of the plate-carrying cylinder and rotatably guided about the longitudinal axis thereof by a drive mechanism so that it is alignable relative to two limiting directions corresponding to two limit positions of the hook, namely, a forward limit position for, respectively, hooking onto and unhooking from an edge of the printing plate in the elongated slot, and a rear limit position for bracing an edge of an end of the printing plate.
From the French Patent FR 2 709 090 that has the same corporate assignee as that of the instant application, such a device has become known heretofore wherein the drive mechanism includes a membrane that is inflatable with pressure medium.
However, a disadvantage of this system is that the membrane has a limited service life and a long response time for the supplying of the pressure medium.
Moreover, with the system described in the aforementioned French Patent FR 2 709 090, it is not possible to adjust the clamping of the top or leading edge of the printing plate by using the hook means, and to adjust the tension of this printing plate that is mounted on the plate-carrying cylinder.
Furthermore, in a different embodiment of the aforementioned French Patent FR 2 709 090, a system with wedges actuated by inflating a membrane is provided. This type of wedge system forming drive mechanisms for actuating the tension rod has a main disadvantage in that the wedges are displaceable in a support rod and, when a major deformation of this rod occurs, poor guidance of the wedges and poor functioning of the drive mechanism result. The support rod for the wedges has a large cross section. The number of wedges must be very high if they are to perform the mechanical action thereof.
It is accordingly an object of the invention to provide a retainer for a printing plate on a plate-carrying cylinder of a rotary printing press that overcomes the foregoing disadvantages heretofore known in the state of the art.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a retainer for firmly holding a printing plate on a plate-carrying cylinder of a rotary printing press, having a hook engageable in an elongated slot formed in the plate-carrying cylinder and terminating in an outer circumferential surface thereof, the hook being fixedly connected to a tension rod that is rotatably supported in a first elongated bore of the plate-carrying cylinder, and a drive mechanism for rotatably guiding the tension rod about the longitudinal axis thereof so that it is alignable relative to two limiting directions corresponding to two limit positions of the hook, including a forward limit position for, respectively, hooking onto and unhooking from an edge of the printing plate in the elongated slot, and a rear limit position for bracing an edge of an end of the printing plate, comprising a piston rod forming part of the drive mechanism, the piston rod being supported in a second longitudinal bore formed in the plate-carrying cylinder, a lever system connecting the piston rod at both ends thereof to the tension rod, the piston rod carrying a plurality of pistons distributed over the length thereof, and a longitudinal conduit selectively suited for supplying pressure medium for positioning the pistons selectively in two extreme positions wherein, in an extended position of the pistons, the latter protrude from the outside of the piston rod so as to place the piston rod in a lower position corresponding to the front limit position of the hook and, in a retracted position of the pistons, the latter are retracted into the piston rod so as to place the piston rod in an upper position corresponding to the rear limit position of the hook.
In accordance with another feature of the invention, the pistons of the piston rod are always braced against a wall defining the second longitudinal bore of the plate-carrying cylinder.
In accordance with a further feature of the invention, the piston rod is mounted in connection levers for connecting the tension rod through an eccentric construction that permits positioning in accordance with a selected orientation of the connection levers with respect to a horizontal axis passing through the longitudinal axes of the piston rods and the tension rods, the orientation corresponding to a fixed orientation of the hook with respect to the horizontal axis.
In accordance with an added feature of the invention, the eccentric construction enables a positioning of the connection lever so that it forms an angle a of approximately 0.+-.1.degree. with the horizontal axis.
In accordance with an additional feature of the invention, each piston of the piston rod is positioned in a somewhat sleeve-shaped jacket and is releasably mounted in a bearing support of the piston rod.
In accordance with yet another feature of the invention, each piston of the piston rod includes a head formed with an inner chamber seated in a bearing support of the piston rod that communicates with a pressure medium supply conduit, the head being mounted with given play displaceably on a shaft in the bearing support of the piston rod, a restoring spring resting on the shaft and having one end that abuts a marginal ridge of the shaft, and another end abutting a component for mounting the head on the shaft, the piston being movable outwardly into a position wherein it protrudes from the piston rod and leads to a compression of the restoring spring, when an inflow of pressure medium into the inner chamber of the head takes place.
In accordance with yet a further feature of the invention, the shaft of each piston of the piston rod is pierced by a conduit terminating at one end in an upper portion of the inner chamber, and terminating at the other end thereof in the bearing support of the piston rod receiving the respective piston, so that at least some of the pressure medium that flows into the bearing support of the piston rod quickly moves upwardly through the conduit in the piston shaft into the upper portion of the inner chamber.
In accordance with yet an added feature of the invention, the elongated gap of the plate-carrying cylinder is defined at front and rear, respectively, with respect to the direction of rotation of the plate-carrying cylinder, by a front longitudinal side and a rear longitudinal side, each front and rear side being oriented, relative to the outer circumferential surface of the plate-carrying cylinder, so that, in the front portion of the connection thereof to the first longitudinal bore of the plate-carrying cylinder, the elongated gap adjoins the first longitudinal bore with respect to the direction of rotation of the cylinder, and the rear side, upon connection with the outer circumferential surface of the plate carrying cylinder, forms a wedge.
In accordance with yet an additional feature of the invention, the front longitudinal axis of the gap in the direction of rotation of the plate-carrying cylinder includes a forward-directed shoulder against which the hook is braced in a front limit position thereof and, in this position and in the rear limit position thereof, the hook remains inside the elongated gap of the plate-carrying cylinder, retreating from the outer circumferential surface of the plate-carrying cylinder.
In accordance with still another feature of the invention, the drive mechanisms include a torsion rod coaxial with the tension rod, the torsion rod being inclined towards the limit orientation thereof corresponding to the rear limit position of the hook, for resilient stressing of the torsion rod.
In accordance with a concomitant feature of the invention, for connecting the piston rod to the tension rod, upon a lowering movement of the piston rod into the second longitudinal bore of the plate-carrying cylinder, the connection lever includes a stop screw coming to a stop against a counterpart stop screw, the stop screw being built into the plate-carrying cylinder for limiting the lowering movement and thus the pivoting path of the connection levers.
Other especially advantageous features of the device according to the invention are as follows:
The pistons of the piston rod are always braced against the wall of the second longitudinal bore of the plate carrying cylinder.
The piston rod is mounted in connection levers through an eccentric construction, which enables the positioning in accordance with a selected orientation of the connection levers with respect to a horizontal axis that passes through the longitudinal axes of the piston and tension rods, this orientation corresponding to a fixed orientation of the hook means with respect to the horizontal axis.
As a result, this eccentric construction advantageously makes it possible to eliminate the clamping changes that have arisen from the interplay of geometric and dimensionally correct errors in the embodiment of the plate-carrying cylinder and the printing plate retainer, and assures optimal clamping of the head edge of the printing plate upon engagement with the longitudinal gap in the plate-carrying cylinder.
To this end, the eccentric construction makes it possible to position the connection levers so that it forms an angle with the horizontal axis of approximately 0.+-.1.degree..
Furthermore, each piston of the piston rod is positioned according to the invention in a somewhat sleeve-shaped jacket and is releasably mounted in a receptacle of the piston rod.
The use of a detachable jacket is especially advantageous, because it makes it possible to compensate for the errors that occur in machining the piston bearings for receiving the pistons of the piston rod. This then makes it possible to reduce the production costs for such a piston rod to such an extent that the machining precision of these receptacles can be reduced.
Furthermore, these jackets make it possible to compensate for the possible play that occurs in the deformation of the piston rod when it is in motion.
Each piston of the piston rod of the retainer according to the invention includes a head with an inner chamber that terminates in a bearing of the piston rod communicating with the pressure medium supply conduit, the head being mounted with a given play displaceably on a shaft in the bearing of the piston rod, a restoring spring being disposed on the shaft and having one end thereof abutting a marginal ridge of the shaft and the other edge thereof abutting a component for the head on the shaft, so that the inflow of pressure medium into the inner chamber of the head of the piston causes the latter to move outwardly into a position wherein it protrudes from the piston rod, and leads to the compression of the restoring spring.
Advantageously, the shaft of each piston of the piston rod of the retainer according to the invention is pierced by a conduit which, at one end, terminates in the upper portion of the inner chamber of the head of the piston and, at the other end, terminates in the bearing support of the piston rod receiving the piston, so that at least some of the pressure medium that flows into the bearing support of the piston rod quickly moves upwardly through the conduit in the piston shaft into the upper portion of the inner chamber of the head of the piston.
Consequently, with the conduit of the piston shaft of each piston, it is possible to attain a maximum stroke of the piston heads immediately after putting the piston rod under pressure.
Each connection lever for connecting the piston rod to the tension rod includes a stop screw, that comes into contact with a counterpart stop screw, that is built into the plate-carrying cylinder, during the lowering movement of the piston rod into the second longitudinal bore of the plate-carrying cylinder, in order to limit this motion and thus the pivoting path of the connection levers.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a retainer for a printing plate on a plate-carrying cylinder of a rotary printing press, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: